The mineral and/or organic particulate feedstock can consist of a mixture of different populations in grain size and/or in nature, making it possible to increase both the number of connections between the layers of the fibrous network constituting the non-woven product and optionally the size of the connecting points between filaments or fibers.
In the above-mentioned field, the current trend is toward the production of new non-woven products either by reduction of components, or by the use of products that are less elegant, but are durable or renewable or recyclable, or else have lower-energy contents, for economic or environmental reasons.
At the same time, the drive to lower production costs is pushing manufacturers to produce faster and faster, while at the same time meeting increasingly high requirements.
The mechanical and hot stability properties of the non-woven products that are used as frames become absolutely decisive factors, as much for their suitability for transformation during the formation of bitumens or hot treatments under analogous constraints, because of a thermal memory effect, as well as relative to the requirements of quality and durability in the final application.
Currently, these frames frequently consist of a non-woven fabric of 80 g/m2 to 350 g/m2 that can be linked and stabilized chemically in the case of a homopolymer substrate or thermally in the case where surfaces are used that consist of two polymers by the melting of one of them.
In some cases, these non-woven surfaces or products can be reinforced by wires, grids, fabrics or glass or synthetic polymer woven materials with very high moduli, before optionally being used as frames that are designed to be impregnated and coated using bitumens that are modified by polymers or other substrates or to undergo transformations under thermal constraints.
In a general way, these surfaces, after being layered following wet, dry or molten production processes that are known to one skilled in the art, undergo intermixing by mechanical needling or by hydraulic binding before their thermal and/or chemical consolidation so as to ensure at least partial cohesion of the fibrous network and thus to impart to it the bulk of its rupture strength.
The chemical or thermal binding that subsequently occurs has as its objective to make the non-woven surface or product dimensionally stable relative to the thermomechanical constraints to which the surface or the product can be subjected.
A possible additional reinforcement of these textiles, by wires, grids or glass or polymer woven materials with very high moduli, incorporated before the mechanical or hydraulic or chemical binding or during the layering, has as its objective to reduce even further its deformability under hot stress (at the post-treatment or transformation temperature) of these thus stabilized fibrous structures.
Actually, these non-woven surfaces or products in layers require high dimensional stability both in place and in aging. Moreover, during their production or transformation, they simultaneously undergo mechanical and thermal constraints with intensities that are quite higher than those undergone during use or final implementation.
Numerous types of non-woven products, meeting in a more or less satisfactory manner the above-mentioned requirements as well as their production processes, have already been proposed and are known in the field.
Thus, the French Patent FR 88 16711 describes a process for the production of a substrate based on non-woven material for a flat article of good dimensional stability that can be linked chemically or thermally, having a weight of between 20 and 500 g/m2, and reinforced longitudinally by continuous threads with high moduli, preferably greater than 50 GPa. In the resulting non-woven product, the breaking of glass threads occurs, under a temperature of 180° C., and under a constraint of at least 80 N per meter of width, and the modulus under cold conditions is the same with or without a reinforcing thread. The dimensional stability under hot conditions and the deformability are thus essentially enhanced relative to standard non-woven products.
The composition as well as the cross-linking mechanism at approximately 200° C. of aqueous chemical binders for non-woven products used in the industry of sealing frames are known by the document U.S. Pat. No. 6,221,973. These binders consist of mixtures of a polyacid that contains at least two carboxylic groups, one polyalcohol that contains at least two hydroxylic groups, and an accelerator.
So as to meet new international standards, the resulting resin that forms a binder disclosed by this US document is substantially free of formaldehyde. This resin is impregnated on a non-woven substrate made of glass fibers that is designed for the production of bitumen-containing coatings. With the glass fibers themselves being insensitive to the temperature range encountered during asphalt application, the essential function of the binder is then to ensure the cohesion of fibers by the solidity and adhesion of the chemical bond points, so as to prevent a mechanical shrinkage of the surface by developing an acceptable resistance, whereby the surface is not consolidated in advance.
Unlike frames made of polyester and more generally the non-woven products made of thermoplastic polymers, the glass fibers or threads that compose the structure that is described in this US document do not undergo structural modifications that are linked to the high stresses and temperatures that are exerted, which can then produce residual shrinkage behavior during the thermal cycles that occur during use.
Numerous other examples of binders that make it possible to consolidate non-woven surfaces are known in the prior art, for example by the documents U.S. Pat. No. 4,076,917, EP 0 583 086, and WO 97/31036.
Certain recent applications or product/market requirements simultaneously demand a very good dimensional stability combined with an increase of the thickness of the non-woven products.
With technical and economic constraints not always allowing an increase of the surface weight, it is then necessary to act on a reduction of the density of the product, generally located in a range of 0.15 to 0.3, or approximately 70 to 80% of vacuum based on the material to be linked.
It is readily understood that this increase of thickness with constant grammage negatively influences the number as well as the size of the connecting points by the increase of the distances between filaments or fibers of layers that are superposed along the Z-axis, and consequently negatively influences the stability and/or the modulus of the non-woven product concerned.
The documents U.S. Pat. No. 6,299,936 and EP 1 664 418 cite the use of cross-linkable resins in aqueous dilution of 40% to 95%, optionally supplemented with mineral feedstocks such as boron, glass silicates or fibers, for the purpose of the production of very rigid and thick products (>1 cm) that consist of inorganic fibers and that are used in insulation.
These documents also mention applications in relation to the possible consolidation of frames of seals or sublayers of cloth or paper. However, said substrates consist only of glass fibers or filaments and are therefore insensitive to temperature in the fields in question. In addition, said non-woven products are not linked in advance by an intermixing of the hydraulic or mechanical needling type, considerably weakening the network.
Furthermore, the document US 2009/0048371 describes the production of a bitumen-containing sealing membrane on the two surfaces, based on a non-woven fabric made of synthetic or artificial fibers, which is consolidated by a mixture of at least one chemical binder and aluminum hydroxide.
The drying and the cross-linking of the binder are preferably implemented at a temperature of 190° C. to 210° C. for approximately 0.5 minute to approximately 5 minutes and preferably 1.3 to 3.0 minutes. The weight ratio of the dry binder is preferably between 15 and 20% (0.5% to 30%) of the weight of the non-woven product to be linked. Aluminum hydroxide is incorporated with a ratio of 10% to 100% of the ratio of dry chemical binder. The sizes of the aluminum hydroxide particles range from 0.5 μm to 50 μm, and preferably between 0.9 μm and 5 μm. The non-woven layer is then coated or impregnated with bitumen to form the membrane.
This US document claims an enhancement of the failure load and the thermal stability of the surface that is thus produced.
Nevertheless, in the comparative examples cited, a very significant reduction of the failure load and an increase in deformability are noted in particular during the use of 10 parts of calcium carbonate or kaolin.
The document BE 858 986 describes the use of a binder that comprises a mixture of polymer, a binder that is formed by emulsion, and an inert feedstock that is designed to increase the mechanical strength of the fabric. The surface to be linked consists of a mixture of synthetic, natural and/or artificial fibers in light grammages, with cohesion and the final properties of the fabric being ensured only using this binder that sets the fibers for preventing disintegration or enhancing resistance to it.
The mean surface weight of these surfaces is on the order of 25 to 35 g/m2 and the production of heavier surfaces is ensured by superposition and subsequent consolidation of individual surfaces.
The most favorable level of strength reached in terms of traction, even enhanced by the mineral feedstocks that are used, is very low and is on the order of 50 N to 80 N/5 cm calculated for 100 g/m2. These values are to be compared to those of a non-woven product that forms a sealing frame, which are on the order of 5 to 10 times greater, to reach 250 to 350 N/5 cm for the same final weight.
The field of application of the products that are described in this BE document is primarily within the framework of textiles that are almost disposable or are intended for thermal insulation. These non-woven products are unsuitable for use within the framework of sealing frames or thermally stable substrates because of the weakness of the cohesion as well as the level of the mechanical properties obtained. It is also noted that certain feedstocks, such as calcium silicate, generate a loss of strength of the non-woven product.